Edge lit light guides and similar devices are known in the art. US 2011096570, for instance, describes an illumination device comprising a lighting unit. The lighting unit comprises a light source and a substantially flat light guide, arranged to collimate light source light. The light guide has an entrance window, an edge window, a first light guide surface, a second light guide surface, a first side edge and a second side edge. One or more of the first light guide surface and the second light guide surface comprise a plurality of grooves. In this way, latitudinal collimation is obtained.